Report from the Sub-comittee on the environment and health

Treatment frequency index
as a measure of <strong>the</strong> load on
<strong>the</strong> terrestrial environment
Critical loads for plants
and animals in terrestrial
natural areas
8.1.2 Impacts on <strong>the</strong> environment
Pesticides can be ranked solely on <strong>the</strong> basis of <strong>the</strong>ir toxicity to different
organisms. The toxicity can also be expressed as <strong>the</strong> tolerable limit value,
which can be calculated on <strong>the</strong> basis of all species or groups of
organisms or be expressed as a value for <strong>the</strong> most sensitive species. The
intended effect of <strong>the</strong> pesticides in <strong>the</strong> terrestrial environment is direct
and considerable in cultivated areas and <strong>the</strong>ir immediate surroundings.
The effect of herbicides on <strong>the</strong> flora is obvious. The indirect effects on
<strong>the</strong> fauna through impact on <strong>the</strong> primary links in <strong>the</strong> food chain are
described in section 4.2.1.
It is for mammals and birds that we have <strong>the</strong> most complete toxicity data
for <strong>the</strong> terrestrial environment. However, <strong>the</strong> risk of direct poisoning of
humans, o<strong>the</strong>r mammals and birds has been reduced considerably by
reviewing existing substances and changing <strong>the</strong> authorisation scheme for
new pesticides, so that all <strong>the</strong> substances in practice have a low level of
toxicity to vertebrates. It is <strong>the</strong>refore not possible to rank modern Danish
pesticides on <strong>the</strong> basis of <strong>the</strong>ir toxicity to <strong>the</strong>se groups of fauna. That is
because characteristic farmland fauna and, particularly, birds are
considerably more affected by <strong>the</strong> indirect effects of pesticide use. These
indirect effects are related to <strong>the</strong> effect of <strong>the</strong> product on <strong>the</strong> target
organism and on o<strong>the</strong>r species belonging to <strong>the</strong> same group of organisms.
Since <strong>the</strong> indirect effects are <strong>the</strong> most extensive, it is important to include
<strong>the</strong>m in <strong>the</strong> load and risk assessments. The dosage is determined by
means of field trials, <strong>the</strong> aim being to achieve an effect on <strong>the</strong> target
organisms that results in at least 90% reduction of <strong>the</strong> population density.
The recommended field dosage is thus a realistic and accurate indicator
of <strong>the</strong> effect of <strong>the</strong> product in <strong>the</strong> field, compared with <strong>the</strong> toxicity
determined in laboratory tests. The treatment frequency index is based
precisely on <strong>the</strong> recommended field dosage with a view to <strong>the</strong> direct
effect on <strong>the</strong> target organisms. Since <strong>the</strong> target organisms’ related species
– fungi, plants or arthropods – are also affected by fungicides, herbicides
or insecticides, respectively, <strong>the</strong> treatment frequency index is also an
indicator of <strong>the</strong> indirect impact on <strong>the</strong> ecosystem as a consequence of
changes in <strong>the</strong> quantity and type of food in <strong>the</strong> food chains.
It is possible to carry out calculations for each pesticide that show <strong>the</strong>
dosage that will be harmless for most faun and flora in hedges, small
biotopes and o<strong>the</strong>r areas bordering on cultivated areas. This value is
called <strong>the</strong> critical load. It expresses <strong>the</strong> total supply of chemical
substance that is considered to be harmless to <strong>the</strong> environment. The
calculations do not take into account <strong>the</strong> fact that <strong>the</strong>re can be increased
effects <strong>from</strong> applying several substances on <strong>the</strong> same area. Calculations
have only been carried out for a few, selected substances (Jensen, Løkke
1998) because considerable resources are needed to collect and assess
data for all relevant pesticides. Moreover, <strong>the</strong>re are insufficient data for
all pesticides. Calculations for four substances show that <strong>the</strong> critical load
for insecticides and herbicides lies in <strong>the</strong> interval <strong>from</strong> one thousandth
part to one ten-thousandth part of <strong>the</strong> field dosage. A system could
possibly be developed for ranking pesticides’ load on <strong>the</strong> terrestrial
environment on uncultivated land. However, <strong>the</strong> load depends primarily
on how much of each pesticide is used and on spraying practice. If,
however, it were found that <strong>the</strong>re was no great variation in <strong>the</strong> critical
load for different pesticides, <strong>the</strong> most important factors would be <strong>the</strong>
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